1. Field of the Technique
The present technique relates to a positional control technique for seeking and fixing a head of a storage device to a predetermined position on a recording medium.
2. Description of the Related Art
Magnetic storage devices read/write data from/to a magnetic disk with a magnetic head.
To read/write data, the magnetic head position should be adjusted to a predetermined track on the magnetic disk. For that purpose, servo information is recorded in a servo sector in advance with a servo track writer etc., the servo sector being provided between data sectors on the track. At the time of reading/writing data from/to the magnetic disk, the magnetic head is sought to a target track position based on a current position.
After having reached the target track position, the magnetic head is positioned to the center of the track.
After the completion of the positioning process, data is read/written.
The positioning process is carried out based on the servo information read with the magnetic head. However, the magnetic head position varies due to an influence of an external force applied onto an actuator equipped with the magnetic head, for example, a wind pressure, a flexible cable, and the like. To eliminate the influence, a bias current that can eliminate the external force is measured in advance, and the measured value is stored in a table. Upon the positioning process, the bias current is applied to a voice coil motor for driving the actuator to thereby adjust the variation in magnetic head position.
One conceivable calibration measurement of a bias current to adjust the position variation is to measure a bias current just after a positioning process. Resultant bias current values are summarized in a table based on the measurement result. However, in the case of measuring a bias current just after a positioning process, the measured bias current value might be variable, not stable due to a residual vibration. For example, since a vehicle-mounted magnetic storage device or the like has a wide operating temperature range of −30° C. to 85° C., a bias current value measured for calibration purposes just after the completion of seek might vary especially at a low temperature.
Therefore, there is a difference between the varying bias current value and a correct bias current value.